It's hard to fail a test that you know is coming -- it either means you have a real problem or you aren't very smart -- but hundreds of players are tested, so a perfect record is rare.

Last year, University of Nebraska defensive end Randy Gregory was the highest-profile case of a positive test (for marijuana), and it sent his draft stock tumbling from a possible top-10 pick to No. 60 by the Cowboys.

This year, when picks start coming off the board Thursday, no player will have to suffer Gregory's fate.